1. Field of the Invention
The present invention relates to an electron-emitting device including an emitter section composed of a dielectric material, a lower electrode disposed on the lower side of the emitter section, and an upper electrode disposed on the upper side of the emitter section so as to be opposed to the lower electrode with the emitter section therebetween.
2. Description of the Related Art
With respect to the emission of electrons from an emitter section composed of a dielectric material, various theories have been presented in the following non-patent documents: Yasuoka and Ishii, “Pulsed electron source using a ferroelectric cathode”, Oyo Butsuri (Applied Physics), Vol. 68, No. 5, p. 546-550 (1999) [Non-patent Document 1]; V. F. Puchkarev, G. A. Mesyats, “On the mechanism of emission from the ferroelectric ceramic cathode”, J. Appl. Phys., Vol. 78, No. 9, 1 Nov. 1995, p. 5633-5637 [Non-patent Document 2]; and H. Riege, “Electron emission ferroelectrics—a review”, Nucl. Instr. and Meth. A340, p. 80-89 (1994) [Non-patent Document 3].
The present applicant has made various proposals on such an electron-emitting device including an emitter section composed of a dielectric material. Namely, an electron-emitting device that has been proposed by the present applicant includes an emitter section composed of a dielectric material, a lower electrode disposed on the lower side of the emitter section, and an upper electrode disposed on the upper side of the emitter section so as to be opposed to the lower electrode with the emitter section sandwiched therebetween. In this electron-emitting device, a drive voltage is applied between the lower electrode and the upper electrode. Thereby, the polarization of the dielectric material is reversed, and electrons are emitted from fine through-holes provided in the upper electrode.
More specifically, as shown in FIGS. 45 to 48, an electron-emitting device 200 includes an upper electrode 204 and a lower electrode 206 respectively disposed on the upper surface and the lower surface of an emitter section 202. Through-holes 204a are provided in the upper electrode 204. The surface of a peripheral portion of each of the through-holes 204a facing the emitter section 202 is separated at a predetermined distance from the emitter section 202.
First, as shown in FIG. 45, the electron-emitting device 200 is in an initial state in which electrons are not accumulated on the upper side (upper surface) of the emitter section 202. Subsequently, as shown in FIG. 46, when a drive voltage is applied such that the potential of the upper electrode 204 is negative with respect to the lower electrode 206, the polarization of the emitter section 202 is reversed. Due to the polarization reversal, electrons are supplied from the upper electrode 204 toward the emitter section 202 beneath the peripheral portion of the through-holes 204a of the upper electrode 204. As a result, electrons are accumulated on the upper side of the emitter section 202 beneath the peripheral portion of the through-holes 204a. 
Subsequently, as shown in FIG. 47, when a drive voltage is applied such that the potential of the upper electrode 204 is positive with respect to the lower electrode 206, the polarization of the emitter section 202 is reversed again. If such a state continues, as shown in FIG. 48, the electrons accumulated on the upper side of the emitter section 202 are emitted upward (in the positive Z-axis direction) by Coulomb repulsion through the through-holes 204a. 
In the electron-emitting device that has been proposed so far, the diameter of the through-hole 204a is, for example, 100 nm or more because it is generally difficult to form a through-hole 204a that has an extremely fine diameter in the upper electrode 204 and because it has been assumed that if the diameter of the through-hole 204a is extremely fine, the amount of electrons that can be supplied to the upper side of the emitter section 202 from the peripheral portion of the through-holes 204a is decreased, and for other reasons.
In order to increase the amount of electron emission per unit area of the upper surface of the electron-emitting device 200, intense studies have been conducted, for example, the diameter of the through-hole 204a has been changed in a range above 100 nm or the number of through-holes 204a has been increased. However, there has been a limit to the amount of electron emission.
The reason for the fact that the amount of electron emission cannot be increased is assumed that, as understood from equipotential lines shown in FIG. 49, the equipotential lines bulge outward from the through-hole 204a, and thereby electrons are easily supplied from the peripheral portion of the through-hole 204a, but are not easily accumulated in the vicinity of a region beneath the center of the through-hole 204a where the intensity of the electric field is weak.